M2b: Android skeleton, :core:model contract, :domain passing all vectors

Gradle project in android/ with every module of SPEC §6.2 (build-logic convention plugins, version catalog,
architecture check in check), :core:model types and repository interfaces of §14.2.4 and §14.5, :domain
implementing §14.5.2 and §14.5.4 (125 vector cases), scenario-driven fakes with the empty scenario, Room 3
entities and KvittDatabase v1 with exported schema, :app shell with Hilt, en/sv strings with MissingTranslation
as a lint error, Roborazzi goldens of the empty screen in light and dark.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/adapter/fcm/build.gradle.kts

@@ -0,0 +1,8 @@
+// :adapter:fcm — Firebase Cloud Messaging, the only module that names the vendor (owned by M8). M2b ships the shell.
+plugins {
+    id("kvitt.android.library")
+}
+
+dependencies {
+    implementation(project(":core:model"))
+}

android/adapter/fcm/src/main/kotlin/se/hagstedt/kvitt/adapter/fcm/FcmAdapter.kt

@@ -0,0 +1,10 @@
+package se.hagstedt.kvitt.adapter.fcm
+
+/**
+ * Module shell. M8 adds the FirebaseMessagingService, token registration and the mapping of data messages to the
+ * project's own push events (SPEC §6.2, §14.6), once the Firebase licence and google-services.json are in place.
+ */
+internal object FcmAdapter {
+    /** Push payload version this adapter understands (SPEC §14.6). */
+    const val PAYLOAD_VERSION: Int = 1
+}